<p>One of the most fundamental human needs is fresh air. It has been estimated that people spend comparatively much time in indoor premises. That creates an elevated need for high-quality ventilation systems in buildings. The ventilation airflow rate is recognised as the main parameter for measuring the indoor air quality. It has been shown that the ventilation airflow rates have effects on respiratory diseases, on “sick building syndrome” symptoms, on productivity and perceived air quality. Ventilation is necessary to remove indoor-generated pollutants by diluting these to an acceptable level. The choice of ventilation airflow rate is often based on norms or standards in which the airflow rate is determined based on epidemiological research and field or laboratory measurements. However, the determination of ventilation flow rate is far more complex. Indoor air quality in the occupied zone can be dependent of many factors such as outdoor air quality, airflow rate, indoor generation of pollutants, moisture content, thermal environment and how the air is supplied into the human occupied zone. One needs to acknowledge the importance of air distribution which clearly affects the comfort of occupants. To design a ventilation system which considers all aspects of room ventilation can only be achieved by computer modelling. The objective of this thesis is to investigate air diffusion, indoor air quality and comfort issues by CFD (computational fluid dynamics) modelling. The crucial part of the CFD modelling is to adopt BCs (boundary conditions) for a successful and accurate modelling procedure. Assessing the CFD simulations by validated BCs enabled constructing the ventilation system virtually and various system layouts were tested to meet given design criteria. In parallel, full-scale measurements were conducted to validate the diffuser models and the implemented simplified particle-settling model. Both the simulations and the measurements reveal the full complexity of air diffusion coupled with solid contaminants. The air supply method is an important factor for distribution of heat, air velocity and solid contaminants. The influence of air supply diffuser location, contaminant source location and air supply method was tested both numerically and by measurements to investigate the influence of different parameters on the efficiency of room ventilation. As example of this, the well-known displacement ventilation is not fully able to evacuate large 10 μm airborne particles from a room. Ventilation should control the conditions in the human breathing zone and therefore the ventilation efficiency is an important parameter. A properly designed ventilation system could use less fresh air to maintain an acceptable level of contaminant concentration in the human breathing zone. That is why complete mixing of air is not recommended as the ventilation efficiency is low and the necessary airflow rate is relatively high compared to other ventilation strategies. Especially buoyancy-driven airflows from heat sources are an important part of ventilation and should not be hampered by supply airflow from the diffusers. All the results revealed that CFD presently is the only reliable method for optimising a ventilation system considering the air diffusion and contaminant level in all locations of any kind of room. The last part of the thesis addresses the possibility to integrate the CFD modelling into a building design process where architectural space geometry, thermal simulations and diffuser BCs could be embedded into a normal building design project.</p>

One of the most fundamental human needs is fresh air. It has been estimated that people spend comparatively much time in indoor premises. That creates an elevated need for high-quality ventilation systems in buildings. The ventilation airflow rate is recognised as the main parameter for measuring the indoor air quality. It has been shown that the ventilation airflow rates have effects on respiratory diseases, on “sick building syndrome” symptoms, on productivity and perceived air quality. Ventilation is necessary to remove indoor-generated pollutants by diluting these to an acceptable level. The choice of ventilation airflow rate is often based on norms or standards in which the airflow rate is determined based on epidemiological research and field or laboratory measurements. However, the determination of ventilation flow rate is far more complex. Indoor air quality in the occupied zone can be dependent of many factors such as outdoor air quality, airflow rate, indoor generation of pollutants, moisture content, thermal environment and how the air is supplied into the human occupied zone. One needs to acknowledge the importance of air distribution which clearly affects the comfort of occupants. To design a ventilation system which considers all aspects of room ventilation can only be achieved by computer modelling. The objective of this thesis is to investigate air diffusion, indoor air quality and comfort issues by CFD (computational fluid dynamics) modelling. The crucial part of the CFD modelling is to adopt BCs (boundary conditions) for a successful and accurate modelling procedure. Assessing the CFD simulations by validated BCs enabled constructing the ventilation system virtually and various system layouts were tested to meet given design criteria. In parallel, full-scale measurements were conducted to validate the diffuser models and the implemented simplified particle-settling model. Both the simulations and the measurements reveal the full complexity of air diffusion coupled with solid contaminants. The air supply method is an important factor for distribution of heat, air velocity and solid contaminants. The influence of air supply diffuser location, contaminant source location and air supply method was tested both numerically and by measurements to investigate the influence of different parameters on the efficiency of room ventilation. As example of this, the well-known displacement ventilation is not fully able to evacuate large 10 μm airborne particles from a room. Ventilation should control the conditions in the human breathing zone and therefore the ventilation efficiency is an important parameter. A properly designed ventilation system could use less fresh air to maintain an acceptable level of contaminant concentration in the human breathing zone. That is why complete mixing of air is not recommended as the ventilation efficiency is low and the necessary airflow rate is relatively high compared to other ventilation strategies. Especially buoyancy-driven airflows from heat sources are an important part of ventilation and should not be hampered by supply airflow from the diffusers. All the results revealed that CFD presently is the only reliable method for optimising a ventilation system considering the air diffusion and contaminant level in all locations of any kind of room. The last part of the thesis addresses the possibility to integrate the CFD modelling into a building design process where architectural space geometry, thermal simulations and diffuser BCs could be embedded into a normal building design project. / QC 20101007

This Thesis deals with the fans, their properties and characteristics. The Project part is about design of the HVAC equipment in the centralised and decentralised option for the assigned building. The Project part is focused on the design and evaluation of the fans more specifically. The Experimental part is about measurement of parameters and characteristics of the fans. The results are analyzed and compared. The results are compared with current energy efficiency reguirements for fans.

La performance d’un système doit être bien définie, atteignable et surtout mesurable. Ce n’est pas le cas aujourd’hui pour la ventilation. D’une part, les performances des systèmes de ventilation sont habituellement exprimées sur des considérations énergétiques ou tout simplement sur une estimation trop approximative des débits de ventilation. Les performances liées au confort thermique et à la qualité de l’air intérieur sont abordées séparément à travers des outils d’évaluation dédiés. D’autre part, les outils d’évaluation existants sont aujourd’hui limités dans leur mise en pratique pour des mesures in situ, notamment lorsqu’il s’agit de ventilation naturelle et mixte. L’objectif de cette thèse est alors d’examiner et d’expérimenter les techniques expérimentales existantes à échelle réelle afin de proposer des améliorations sur les méthodes d’évaluation et de commissionnement. La thèse aborde la performance de la ventilation en prenant en compte l’efficacité de ventilation comme performance intrinsèque et le confort thermique comme performance globale.La première partie est consacrée à l’évaluation in situ des performances intrinsèques de ventilation (taux de ventilation, âges moyens de l’air et efficacité de renouvellement d’air), en se basant sur des techniques de gaz traceurs. Après une analyse théorique des différents indicateurs de performance de ventilation et de leurs techniques de mesure correspondantes, une étude expérimentale a été menée dans une salle de cours sous différentes stratégies de ventilation (mécanique, naturelle et mixte). Les analyses ont démontré l’importance de la mise en application des techniques de décroissance de gaz traceurs sur l’incertitude des taux de renouvellement d’air avec notamment une forte influence des temps de mesure et des concentrations de gaz utilisées. Une méthodologie a été adaptée puis testée pour la mesure de l’efficacité de renouvellement d’air en ventilation mécanique, naturelle et mixte en s’affranchissant de mesures en bouches d’extraction (technique habituellement utilisée et préconisée par les normes).La deuxième partie est consacrée à l’évaluation expérimentale in situ du confort thermique sous différentes configurations de ventilation. Différentes méthodes, standards et techniques d’évaluation ont été testés et comparés avec la perception des occupants. Les résultats ont démontré la présence de plusieurs inadéquations lors de la mise en pratique des méthodes et normes existantes. Principalement, il s’agit de l’inadéquation des méthodes statiques (PMV PPD) pour l’évaluation du confort en présence de conditions thermiques fluctuantes, y compris en ventilation mécanique. Les analyses d’incertitudes liées aux erreurs de mesure ont démontré l’incohérence des normes actuelles dans la classification des catégories de confort. / The performance of a system must be well defined, attainable and above all measurable. This is not the case today for ventilation. On the one hand ventilation performance is usually declined on energy efficiency considerations or simply on a rough estimation of ventilation rates. The performance related to thermal comfort and IAQ are addressed separately through dedicated evaluation tools. On the other hand, the existing evaluation tools today are nowadays limited in their practical applications for in situ measurements, in particular in the case of natural and mixed ventilation. The aim of the present thesis is to examine the existing experimental technics, at full scale building in order to propose improvements on evaluation methods and commissioning protocols. The present thesis deals with ventilation performance taking into account ventilation efficiency as intrinsic performance and thermal comfort as overall performance.The first part is devoted to the in situ assessment of intrinsic ventilation performance (ventilation rates, mean age of air, and air exchange efficiency), based on decay tracer gas techniques. After a theorical analysis of the various performance indexes and their corresponding measurement techniques, an experimental study was carried out in a classroom under different ventilation strategies (mechanical, natural & mixed mode). The analysis proved the importance of the application of the tracer gas decay on ventilation rates accuracy with in particular a strong influence of measurement times and used tracer gas concentration. A methodology has been adapted and tested for the measurement of the air exchange efficiency in natural and mixed mode ventilation, by avoiding measurements in exhaust vents (a technique usually used and advocated by current standards).The second part is devoted to in situ assessment of thermal comfort under different ventilation strategies. Different methods, standards and evaluation techniques were tested and compared with occupants’ perception. The results demonstrated the presence of several inadequacies during the implementation of existing methods and standards. Mainly, it concerns the inadequacy of static methods (PMV PPD) for thermal comfort assessment in the presence of fluctuating thermal conditions, even with mechanical ventilation. Uncertainty analysis related to measurement errors has demonstrated the incoherence of current standards in the classification of comfort categories.